OUTBREAKS OF HYPERKERATOTIC DERMATITIS OF ATHYMIC NUDE-MICE IN NORTHERN ITALY

Hyperkeratotic dermatitis of athymic nude mice is an infectious diseas e caused by a coryneform bacterium. During the spring of 1995, outbrea ks of hyperkeratotic dermatitis were observed in several nude mice fac ilities in northern Italy. In this report we describe the clinical, hi stopathological and microbiological features of the disease in two dif ferent animal facilities. Affected animals showed a typical 'scaly' ap pearance with small white flakes of material adherent to the skin. In one of the outbreaks (facility 2) the lesions were less severe and inv olved only Limited areas of the body. The infection spread very quickl y and the morbidity reached more than 80% in a few days, while the mor tality was about 1%. The lesions resolved spontaneously within 7-10 da ys. Histological examination of affected skin revealed orthokeratotic hyperkeratosis, acanthosis and dermal inflammatory infiltration which were more severe in mice from facility 1. In Gram-stained sections gro ups of rods consistent with coryneform bacteria were detectable in the keratin layers covering the epidermal surface. A coryneform bacterium , biochemically typed as Corynebacterium bovis, was isolated from 11 o ut of 11 mice from facility 1 and from 8 out of 11 mice from facility 2.